Hindawi Publishing Corporation The Scientific World Journal Volume 2013, Article ID 652124, 7 pages http://dx.doi.org/10.1155/2013/652124

Research Article Solvation Effects on the Static and Dynamic First-Order Electronic and Vibrational Hyperpolarizabilities of Uracil: A Polarized Continuum Model Investigation Andrea Alparone Department of Chemistry, University of Catania, Viale A. Doria 6, Catania 95125, Italy Correspondence should be addressed to Andrea Alparone; [email protected] Received 27 August 2013; Accepted 18 September 2013 Academic Editors: T. S. Chu, T. Ebata, P. Orea, and R. Schweiss Copyright © 2013 Andrea Alparone. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Electronic (𝛽𝑒 ) and vibrational (𝛽V ) first-order hyperpolarizabilities of uracil were determined in gas and water solution using the Coulomb-attenuating Density Functional Theory level with the Dunning’s correlation-consistent aug-cc-pVDZ basis set. Frequency-dependent 𝛽𝑒 values were computed for the Second Harmonic Generation (SHG) and Electric Optical Pockels Effect (EOPE) nonlinear optical phenomena. The Polarized Continuum Model was employed to study the solvent effects on the electronic and vibrational properties. The introduction of solvation contributions increases the 𝛽𝑒 (static) value by ca. 110%. In comparison, smaller enhancements are found for the 𝛽𝑒 (EOPE) and 𝛽𝑒 (SHG) data evaluated at the typical wavelength of 694 nm (by 40–50%). The gas-water hyperpolarizability difference was rationalised through a density analysis study. The magnitudes of the vibrational first-order hyperpolarizabilities are comparable to their electronic counterparts and noticeably increase in solution: 𝛽V (EOPE) ∼ 𝛽𝑒 (EOPE) in aqueous phase at 𝜆 = 694 nm. Analysis of the IR and Raman spectra is useful to elucidate the most important contributing modes to the vibrational first-order hyperpolarizabilities.

1. Introduction Organic nonlinear optical (NLO) compounds are intensively studied, primarily for their potential use in the design of photonic and optoelectronic devices [1–3]. Biomolecules are attractive NLO materials, having the practical advantage to be already available in nature. Over recent years, DNA-based systems have received great attention for their conductive and NLO applications [4–12]. Nevertheless, characterization of the NLO properties of single nucleic acid bases is still rather incomplete. To the best of our knowledge, experimental response electric properties of the smallest base uracil are not available so far, whereas some theoretical estimates of the electronic polarizabilities (𝛼𝑒 ) [13–21] and secondorder hyperpolarizabilities (𝛾𝑒 ) [18] were previously reported. However, there is significant interest in exploring the secondorder NLO effects, which are important for immediate practical applications. At the microscopic level, the secondorder NLO properties are associated with the first-order hyperpolarizability tensor (𝛽𝑖𝑗𝑘 ), which originates from the

responses of a molecular system to external electric field strengths F𝑖 , producing an induced dipole moment 𝜇𝑖 (𝐹𝑖 ): 𝜇𝑖 (𝐹𝑖 ) = 𝜇𝑖 (0) + 𝛼𝑖𝑗 𝐹𝑗 +

1 1 𝛽 𝐹 𝐹 + 𝛾 𝐹 𝐹 𝐹 + ⋅⋅⋅ . 2! 𝑖𝑗𝑘 𝑗 𝑘 3! 𝑖𝑗𝑘𝑙 𝑗 𝑘 𝑙 (1)

Recently, pure vibrational contributions to the first-order hyperpolarizability of uracil have been calculated in vacuum through a Lanczos procedure [22], whereas explorations of solvent effects on the electronic and vibrational 𝛽 values are still lacking to date. Our current computational study mainly focuses on the electronic (𝛽𝑒 ) and vibrational (𝛽V ) static and dynamic firstorder hyperpolarizabilities of uracil. The fundamental role of the vibrational counterparts to the hyperpolarizabilities has been widely documented [23]. The present calculations were performed in gas and water solution under the Polarized Continuum Model (PCM) approximation [24, 25]. There are many indications in the literature showing that calculated

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first-order hyperpolarizabilities of organic molecules are strongly affected by solvent contributions [26–33]. Solvation effects on the electronic and vibrational 𝛼 [18, 19] and 𝛾 [18] values of uracil have been previously explored by means of PCM Hartree-Fock and DFT computations in carbon tetrachloride, acetonitrile, and water solutions.

2. Computational Methods The present calculations were performed in the gas phase and water solution (𝜀 = 78.3553) with the Gaussian 09 package [34]. The solvent effects were entirely modelled under the PCM approximation as implemented in the Gaussian 09 program. The geometry of uracil was optimized under the planar 𝐶𝑠 symmetry using the CAM-B3LYP functional [35] and the polarised and diffuse Dunning’s correlation-consistent augcc-pVDZ basis set [36]. The IR and Raman spectra were simulated under the harmonic approximation at the CAMB3LYP/aug-cc-pVDZ level on the geometries optimized at the same level. The structures are true minima on the potential energy surfaces (no imaginary wavenumbers). Static 𝛽𝑒 values were calculated at the CAM-B3LYP/augcc-pVDZ//CAM-B3LYP/aug-cc-pVDZ level. We selected the CAM-B3LYP functional and aug-cc-pVDZ basis set considering their satisfactory performances in the prediction of the response electric properties of organic compounds, reproducing adequately first-order hyperpolarizabilities obtained using high-level correlated ab initio methods and larger basis sets [28, 29, 37–45]. The dynamic electronic firstorder hyperpolarizabilities [𝛽𝑒 (−𝜔𝜎 ; 𝜔1 , 𝜔2 )] for the Second Harmonic Generation [SHG, 𝛽𝑒 (−2𝜔; 𝜔, 𝜔)] and Electric Optical Pockels Effect [EOPE, 𝛽𝑒 (−𝜔; 𝜔, 0)] NLO phenomena were calculated at the CAM-B3LYP/aug-cc-pVDZ level in the ℏ𝜔 range 0–0.06563 a.u. The highest ℏ𝜔 value corresponds to the wavelength (𝜆) of 694 nm, which is characteristic of the ruby laser. Static pure vibrational first-order hyperpolarizabilities were obtained at the CAM-B3LYP/aug-cc-pVDZ//CAMB3LYP/aug-cc-pVDZ level in vacuum and water solution under the double-harmonic approximation (the used symbols have their standard meaning) [23]: V = [𝜇𝛼] 𝛽𝑖𝑗𝑘 3𝑁−6

0,0

= ∑ (( 𝑎

𝜕𝛼𝑗𝑘 𝜕𝜇𝑗 𝜕𝜇𝑖 𝜕𝛼 )( ) +( ) ( 𝑖𝑘 ) 𝜕𝑄𝑎 0 𝜕𝑄𝑎 0 𝜕𝑄𝑎 0 𝜕𝑄𝑎 0 +(

(2)

𝜕𝛼𝑖𝑗 −1 𝜕𝜇𝑘 )( ) ) × (𝜔𝑎2 ) . 𝜕𝑄𝑎 0 𝜕𝑄𝑎 0

By assuming the validity of the infinity frequency approximation [46], the 𝛽V (SHG) and 𝛽V (EOPE) processes are, respectively, V 𝛽𝑖𝑗𝑘 (−2𝜔; 𝜔, 𝜔)𝜔 → ∞ = 0,

1 0,0 V 𝛽𝑖𝑗𝑘 (−𝜔; 𝜔, 0)𝜔 → ∞ = [𝜇𝛼] . 3

(3)

Table 1: Dipole moments 𝜇 (D) and static electronic first-order hyperpolarizabilities 𝛽𝑒 (a.u.) of uracila . 𝜇𝑥 𝜇𝑧 𝜇 𝑒 𝛽𝑥𝑥𝑥 𝑒 𝛽𝑥𝑦𝑦 𝑒 𝛽𝑥𝑧𝑧 𝑒 𝛽𝑧𝑥𝑥 𝑒 𝛽𝑧𝑦𝑦 𝑒 𝛽𝑧𝑧𝑧 𝛽𝑥𝑒 𝛽𝑧𝑒 𝑒 𝛽vec

Gas 1.21 4.41 4.57 (3.87)b 79.3 19.5 5.7 −106.5 −36.5 78.2 104.6 −64.8 123.0

Water 1.88 5.96 6.25 183.9 44.0 24.6 −240.5 −56.4 262.3 252.5 −34.6 254.9

a

Calculations were carried out at the CAM-B3LYP/aug-cc-pVDZ level on the geometry calculated at the same level. b Reference [48].

In this study we report the invariant first-order hyperpolarizabilities (𝛽vec ) [47]: 𝛽vec = √𝛽𝑥2 + 𝛽𝑦2 + 𝛽𝑧2 ,

(4)

where 𝛽𝑖 (𝑖 = 𝑥, 𝑧) is given by 𝛽𝑖 = (1/3) ∑𝑗=𝑥,𝑦,𝑧 (𝛽𝑖𝑗𝑗 + 𝛽𝑗𝑖𝑗 + 𝛽𝑗𝑗𝑖 ). Atomic units are used throughout the work. Conversion factor to the SI is: 1 a.u. of 𝛽(𝑒3 𝑎03 𝐸ℎ−2 ) = 3.206361 × 10−53 C3 m3 J−2 .

3. Results and Discussion Table 1 lists the CAM-B3LYP/aug-cc-pVDZ dipole moments. The largest 𝜇 component lies along the z-axis, recovering ca. 96% of the total 𝜇 value. The gas phase 𝜇(CAM-B3LYP/augcc-pVDZ) of 4.57 D overestimates by 18% the experimental datum obtained by microwave measurements [𝜇(exp.) = 3.87 D] [48], being in good agreement with the high-level ab initio CCSD(T)/aug-cc-pVDZ estimate of 4.33 D (+5.5%) [19]. The introduction of the solvation contributions increases the 𝜇 value by 1.4 D (+37%), in qualitative consistency with the observed increase of 0.26 D when passing from the gas phase [48] to dioxane solution [49]. Table 1 also includes the static electronic first-order hyp𝑒 (𝑖 = 𝑥, 𝑧; 𝑗 = 𝑥, 𝑦, 𝑧) erpolarizability tensor components 𝛽𝑖𝑗𝑗 𝑒 is in absolute in gaseous and aqueous phases. In gas, 𝛽𝑧𝑥𝑥 value the predominant component (−106.5 a.u.), whereas in 𝑒 (−240.5 a.u.) water solution the largest components are 𝛽𝑧𝑥𝑥 𝑒 and 𝛽𝑧𝑧𝑧 (262.3 a.u.). When passing from the gas phase to the water solution, the 𝛽𝑥𝑒 value increases by about a factor of two, whereas on the contrary |𝛽𝑧𝑒 | decreases by ca. a factor of two. From the present computations, 𝛽𝑥𝑒 dominates the first-order hyperpolarizability of both the gaseous and aqueous phases, 𝑒 value, respectively. giving ca. 85% and 99% of the 𝛽vec In order to clarify the solvation effects on the response electric properties, we determined the spatial contributions of

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electrons to the first-order hyperpolarizabilities by comput(2) ing density of hyperpolarizability amplitudes, 𝜌𝑗𝑘 (𝑟) [50, 51]. (2) The 𝜌𝑗𝑘 (𝑟) is defined as derivative of the charge density function 𝜌(𝑟, 𝐹) with respect to applied electric field strengths 𝐹 (𝑟 is the position vector). The 𝜌(𝑟, 𝐹) is usually expanded in powers of 𝐹:

𝜌 (𝑟, 𝐹) = 𝜌(0) (𝑟) + ∑ 𝜌𝑗(1) (𝑟) 𝐹𝑗 + 𝑗

+

1 ∑ 𝜌(2) (𝑟) 𝐹𝑗 𝐹𝑘 2! 𝑗 𝑗𝑘

1 ∑ 𝜌(3) (𝑟) 𝐹𝑗 𝐹𝑘 𝐹𝑙 + ⋅ ⋅ ⋅ , 2! 𝑗 𝑗𝑘𝑙

(2) 𝜌𝑗𝑘 (𝑟) =

󵄨 𝜕2 𝜌 (𝑟, 𝐹) 󵄨󵄨󵄨󵄨 , 󵄨 𝜕𝐹𝑗 𝜕𝐹𝑘 󵄨󵄨󵄨󵄨𝐹 =0,𝐹 =0 𝑗

𝑒 𝛽𝑖𝑗𝑘 =−

Z

𝑘

1 (2) ∫ 𝑟𝜌𝑗𝑘 (𝑟) 𝑑𝑟. 2!

X

(5) (2) (𝑟) pair, the sign is positive For a certain positive-negative 𝜌𝑗𝑘 when the direction of the positive to negative density is coincident with the positive direction of the chosen coordinate system (Figure 1), whereas the magnitude is proportional to the distance between the two densities. Following the current 𝑒 calculations, the main contribution to 𝛽𝑥𝑒 is given by the 𝛽𝑥𝑥𝑥 component, recovering ca. 75% (64%) and 73% (72%) of 𝑒 ) values in gas and water solution, respectively. the 𝛽𝑥𝑒 (𝛽vec (2) (𝑟) densities at the CAMTherefore, we explored the 𝜌𝑥𝑥 B3LYP/aug-cc-pVDZ level using the numerical procedure previously illustrated by Yamada and coworkers [51]. The results evaluated at the isosurface of 0.25 a.u. are illustrated in Figure 2. As can be appreciated from the graphical (2) (𝑟) distribution in the water solution representations, the 𝜌𝑥𝑥 is almost similar to that predicted in vacuum even if the amplitudes are much more spread out. This result is in some 𝑒 values, with the consistency with the calculated static 𝛽𝑥𝑥𝑥 𝑒 𝑒 𝑒 𝑒 (gas) ratios being 𝛽𝑥𝑥𝑥 (water)/𝛽𝑥𝑥𝑥 (gas) and 𝛽vec (water)/𝛽vec computed to be 2.3 and 2.1, respectively. Note that the above ratios are somewhat greater than those previously predicted for the average 𝛼𝑒 (1.3) and 𝛾𝑒 (1.5) properties by HF/aug-ccpVDZ computations [18]. Figure 3 displays the frequency-dependent first-order hyperpolarizabilities computed in gaseous and aqueous phases in the 0–0.06563 ℏ𝜔 range for the SHG and EOPE NLO processes. It is important to notice that resonance enhancement effects for the SHG phenomenon are expected to be rather marginal, since the experimental lowest-energy absorption being placed at 5.08 eV (0.1867 a.u.) in vapour [52] and 4.77 eV (0.1753 a.u.) in water solution [53] is sufficiently far from the highest 2 ℏ𝜔 value of 0.1307 a.u. Not surpris𝑒 𝑒 (−2𝜔; 𝜔; 𝜔) > 𝛽vec (−𝜔; 𝜔; 0) > ingly, in the gas phase 𝛽vec 𝑒 𝛽vec (0; 0; 0). The dispersion effects evaluated at the ℏ𝜔 = 0.06563 a.u. increase the static values by 13.7% for the EOPE and by 61.5% for the SHG process. On the other hand, in aqueous phase the dispersion effects are significantly reduced, mainly due to incomplete responses of polar solvents as

Figure 1: Structure of uracil and Cartesian coordinate system. Colours: white (hydrogen), grey (carbon), red (oxygen), and cyan (nitrogen) (colour figure online).

X

e 𝛽xxx = 79.3 a.u.

e = 183.9 a.u. 𝛽xxx

(2) Figure 2: Hyperpolarizability density distributions 𝜌𝑥𝑥 (𝑟) of uracil in gas (left) and water solution (right). The yellow and blue (2) (𝑟) surfaces (colour figure online) refer to positive and negative 𝜌𝑥𝑥 densities, respectively, computed at the isosurface of 0.25 a.u. CAMB3LYP/aug-cc-pVDZ results.

modelled by the PCM treatment [31–33, 54]. As can be 𝑒 (−2𝜔; 𝜔; 𝜔) < appreciated from Figure 3, in water solution 𝛽vec 𝑒 𝛽vec (−𝜔; 𝜔; 0) for the ℏ𝜔 values between 0.01 and 0.04 a.u., 𝑒 𝑒 (−2𝜔; 𝜔; 𝜔) ∼ 𝛽vec (−𝜔; 𝜔; 0) at ℏ𝜔 ∼ 0.045 a.u. whereas 𝛽vec It is worth noting that at the ℏ𝜔 value of 0.06563 a.u. the dispersion effect is negative for the EOPE phenomenon, with 𝑒 (−𝜔; 𝜔; 0)(water) value being decreased by ca. 16.0% the 𝛽vec with respect to the static datum. On the other hand, in the case of the SHG process in water solution, the dispersion effect at ℏ𝜔 = 0.06563 a.u. is still positive as for the gas phase, even if it is noticeably inferior (+15.5%). As a consequence, although the static and dynamic electronic first-order hyperpolarizabilities in water solution are greater than the corresponding data in gas (compare the curves in Figure 3), 𝑒 𝑒 (water)/𝛽vec (gas) ratios, the dispersion effects reduce the 𝛽vec which are predicted to be 2.1, 1.53 and 1.48, respectively, for the static, EOPE, and SHG processes at ℏ𝜔 = 0.06563 a.u.

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The Scientific World Journal Table 2: Selected vibrational contributions to the first-order hyperpolarizabilities of uracila .

Gas

Mode no. ]4 ]5 ]11 ]23 ]24 ]25 ]26

Wavenumbers (cm−1 ) 411 524 783 1523 1711 1802 1828

𝐼IR (km/mol) 20 22 4 127 56 902 607

˚ 4 /amu) ARaman (A 1 2 22 11 30 58 29

]5 ]23 ]24 ]25 ]26

530 1527 1699 1721 1769

45 236 159 2086 877

4 42 75 115 116

Water

Descriptionb 𝜏ring 𝛿ring 𝛿ring ]ring + 𝛿N-H ]ring + 𝛿C-H ]C=O + 𝛿N-H ]C=O + 𝛿N-H Total 𝛿ring ]ring + 𝛿N-H ]ring + 𝛿C-H ]C=O + 𝛿N-H ]C=O + 𝛿N-H Total

𝑒 𝛽vec (−𝜔; 𝜔, 0) (a.u.)c 11.5 13.8 10.6 12.5 10.4 57.8 32.4 65.0 (139.8)d 29.5 35.6 29.6 127.2 70.9 193.9 (214.1)d

a

Calculations were carried out at the CAM-B3LYP/aug-cc-pVDZ level on the geometry calculated at the same level. The contributions with percentage ≥15% V of the total 𝛽vec (−𝜔; 𝜔, 0) value were considered. b V: stretching, 𝛿: in-plane bending, 𝜏: torsion. c 𝑒 The value in parentheses refers to the CAM-B3LYP/aug-cc-pVDZ 𝛽vec (−𝜔; 𝜔, 0) value at ℏ𝜔 = 0.06563 a.u. d V 𝑒 The 𝛽vec (−𝜔; 𝜔, 0)/𝛽vec (−𝜔; 𝜔, 0) ratios are 0.46 and 0.91 in gas and water solution, respectively. 300

140

293

e 𝛽vec (a.u.)

250 214 200

199

150

140

 𝛽vec (−𝜔; 𝜔, 0) (a.u.)

120 100 80 60 40 20 0 0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0

1000

EOPE-gas SHG-gas

2000

3000

4000

Wavenumbers (cm−1 )

ℏ𝜔 (a.u.)

EOPE-water SHG-water

Water Gas

Figure 3: Frequency-dependent electronic first-order hyperpolarizability of uracil in gas and water solution. CAM-B3LYP/aug-cc𝑒 (−𝜔𝜎 ; 𝜔1 , 𝜔2 ) values pVDZ results. The reported data refer to the 𝛽vec obtained at ℏ𝜔 = 0.06563 a.u.

Figure 4: Contribution of each normal mode to the vibrational firstorder hyperpolarizability of uracil in gas and water solution. CAMB3LYP/aug-cc-pVDZ results.

Beside the electronic first-order hyperpolarizability, we explored the solvation effects on the pure vibrational counterpart for the EOPE phenomenon. In a recent theoretical study, Christiansen and coworkers have determined the pure vibrational first-order hyperpolarizabilities of uracil in gas using VCI computations and the Lanczos algorithm [22]. However, their reported data refer to the static and SHG process and are not directly comparable to our results. Figure 4 shows the V (−𝜔; 𝜔; 0) data in gaseous CAM-B3LYP/aug-cc-pVDZ 𝛽vec and aqueous phases over the 0–4000 cm−1 wavenumbers

range. The largest contributions originate from the spectral region between 1500 and 2000 cm−1 . Table 2 summarizes the V (−𝜔; 𝜔; 0) values, main vibrational contributions to the 𝛽vec also including the vibrational wavenumbers, IR intensities (𝐼IR ), and Raman activities (ARaman ). The highest-energy region (wavenumbers > 3000 cm−1 ), entirely characterized by C–H and N–H stretching vibrations, furnishes only modV (−𝜔; 𝜔; 0) data, principally owing est contributions to the 𝛽vec to the high-wavenumber values. On the other hand, the lowenergy modes (wavenumbers < 1000 cm−1 ) produce small

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26

25

Figure 5: Atom vector displacements of the ] C=O + 𝛿N-H modes ]25 and ]26 .

1200

1000

Wavenumbers (cm−1 ) 1400 1600

Raman

1800

23

24

23

24

26 25

26 25

IR 1000

1200

1400

1600

vacuum exhibit the strongest absorption peaks in the IR spectrum (Figure 6), with the I IR values of 902 and 607 km/mol, respectively. Note that the ]25 and ]26 modes are also active ˚ 4 /amu, resp.). in the Raman spectra (ARaman = 58 and 29 A V (−𝜔; 𝜔; 0) values originated by the ]25 As a result, the 𝛽vec and ]26 transitions contribute, respectively, to ca. 89% and V (−𝜔; 𝜔; 0) datum. In water solution 50% of the total 𝛽vec (Figure 6), the wavenumbers of the ]25 and ]26 vibrations are downward shifted, respectively, by ca. 80 cm−1 (−4.5%) and 60 cm−1 (−3.2%) with respect to the gas phase, with the I IR values being concomitantly increased by ca. 131% and 45%, respectively. In addition, when passing from the gaseous to the aqueous phase, the ARaman (]25 ) and ARaman (]26 ) values enhance by ca. a factor of two and four, respectively. Therefore as for the 𝛽𝑒 values, the solvent contributions are expected to play a crucial role also for the vibrational first-order V (−𝜔; 𝜔; 0) hyperpolarizabilities of uracil, increasing the 𝛽vec values of the ]25 and ]26 modes by 69.4 a.u. (+120%) and 38.5 a.u. (+119%). As can be appreciated by the data reported V (−𝜔; 𝜔; 0) in Table 2, for both the phases other relevant 𝛽vec contributions are given by the ring stretching modes as well as by the in-plane ring bending deformations, owing to their relatively low wavenumbers and moderate I IR and ARaman values. On the whole, the introduction of solvent V (−𝜔; 𝜔; 0) by ca. 130 a.u., contributions increases the total 𝛽vec V V with the 𝛽vec (−𝜔; 𝜔; 0)(water)/𝛽vec (−𝜔; 𝜔; 0)(gas) ratio being predicted to be ca. three. Finally, it is worth noting that, at ℏ𝜔 = 0.06563 a.u. on going from the gas phase to water soluV 𝑒 (−𝜔; 𝜔; 0)/𝛽vec (−𝜔; 𝜔; 0) ratio is almost doubled, tion, the 𝛽vec increasing from 0.46 to 0.91.

1800

Wavenumbers (cm−1 ) Water Gas

Figure 6: IR and Raman spectra of uracil in gas and water solution in the 1000–1900 cm−1 wavenumbers range. Lorentz line shapes with a full width at half maximum of 10 cm−1 were used. CAMB3LYP/aug-cc-pVDZ results.

V and moderate 𝛽vec (−𝜔; 𝜔; 0) contributions, since the vibrational transitions are rather weak in the IR [I IR ∝(𝜕𝜇𝑖 /𝜕𝑄𝑎 )2 ] and Raman [ARaman ∝ (𝜕𝛼𝑖 /𝜕𝑄𝑎 )2 ] spectra. As for the pure vibrational polarizabilities [19], in both the gas phase V (−𝜔; 𝜔; 0) values originate and water solution, the largest 𝛽vec from the C=O stretching vibrations with the nonnegligible contribution of the in-plane N-H bending deformation (modes ]25 and ]26 ). A graphical representation of the atomic displacement vectors involved in these vibrational modes is displayed in Figure 5. These transitions located at 1802 cm−1 (]25 ) and 1828 cm−1 (]26 ) by the present calculations in

4. Conclusions We have examined the effects of solvation on the static and frequency-dependent electronic and vibrational first-order hyperpolarizabilities of uracil. The properties were modeled in vacuum as well as in water solution using the PCM approach. The calculations were carried out using the longrange corrected CAM-B3LYP functional with the Dunning’s correlation-consistent aug-cc-pVDZ basis set. The introduction of solvent contributions significantly increases both the electronic and vibrational first-order hyperpolarizabilities. However, the dispersion effects on the electronic hyperpolarizabilities for the EOPE and SHG NLO phenomena are noticeably reduced when passing from the gas phase to the water solution. The magnitudes of the vibrational properties are comparable to the electronic counterparts, with the V 𝑒 V /𝛽vec ratio increasing with the solvation and 𝛽vec (water)∼ 𝛽vec 𝑒 𝛽vec (water) for the EOPE process at the characteristic wavelength of 694 nm. The most relevant contributing modes to the 𝛽V values principally involve the very intense infrared C=O stretching + N-H in-plane bending deformation vibrations.

Conflict of Interests The author declares that there is no conflict of interests regarding the publication of this paper.

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